linux-kernel - Re: [PATCH][GIT PULL] tracing: Fix compile issue for trace_sched

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Date:	Fri, 22 Oct 2010 10:13:50 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>, tj@...nel.org
Subject: Re: [PATCH][GIT PULL] tracing: Fix compile issue for
	trace_sched_wakeup.c

On Fri, Oct 22, 2010 at 10:14:31AM +0200, Peter Zijlstra wrote:
> On Thu, 2010-10-21 at 21:44 -0400, Jason Baron wrote:
> 
> > I finally found that we actually continue to run after the above
> > apparent 'hang'. That is, we continue to make progress updating the jump
> > labels. And doing a dump of all the system tasks at the time of the hang
> > showed the processes in various places besides the stop machine threads.
> > Thus, I thought that perhaps, for some reason the stop machine threads
> > weren't being scheduled.
> > 
> > Thus, I tried commenting out the special scheduling that is set up for
> > stop machine threads, and that fixed the hang. I haven't yet looked into
> > what might be going wrong with that scheduling...but maybe somebody else
> > knows...
> 
> Hrmm, so are you saying rq->stop was runnable but not running?

yes, that's what it seems like.

> 
> That would imply broken wakeup-preemption, does something like the below
> cure that?
> 
> 

no still seeing the same hang with the below patch...also, as a data point I
backed out the patch that adds the stop_sched_class and that resolved the hang
as well - just as a data point.

thanks,

-Jason

> ---
>  kernel/sched_stoptask.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/sched_stoptask.c b/kernel/sched_stoptask.c
> index 45bddc0..50ad10f 100644
> --- a/kernel/sched_stoptask.c
> +++ b/kernel/sched_stoptask.c
> @@ -35,6 +35,7 @@ static struct task_struct *pick_next_task_stop(struct rq *rq)
>  static void
>  enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
>  {
> +	resched_cpu(cpu_of(rq));
>  }
>  
>  static void
> 
> 
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